1. Field of the Invention
The invention relates to a semiconductor device manufacturing apparatus for heating or producing a plasma by a high frequency (also including a microwave) electric power.
2. Related Background Art
It is known, for example, as disclosed in "The Study of Semiconductor", edited by Nishizawa, Kogyo Chosa Kai, Vol. 17, page 227 that, a semiconductor device manufacturing apparatus using a high frequency discharge represented by a reactive ion etching (RIE) apparatus is ordinarily constructed in a manner such that a wafer (substrate) for a semiconductor device is exposed to a plasma which is generated by a high frequency electric power. According to such a manufacturing apparatus, a substrate temperature and a substrate potential, as important parameters of the semiconductor processes, are monitored by a simple thermocouple and an electric wire.
According to the conventional apparatus as mentioned above, however, since both of the thermocouple and a susceptor are also exposed to the high frequency electric field together with a wafer, there is a drawback such that it is difficult to accurately perform a measurement. Namely, the temperature and potential of the substrate are generally measured by a voltmeter having a large input impedance. That is, the thermocouple on the input side of the voltmeter or a substrate potential measuring electrode exhibits a high impedance. It is well known that when a portion of a high impedance exists in the high frequency electric field as mentioned above, a large potential change occurs only in the case where only a slight high frequency current flows. Therefore, in order to reduce the high frequency impedance, for example, the use of a low pass filter by a concentrated constant circuit ,comprising an inductance (coils L.sub.1 to L.sub.3) and capacitances (C.sub.1 to C.sub.3) as shown in FIG. 1 has been used. However, the correct effect is not always obtained. In other words, according to an LC filter by the conventional concentrated constant circuit (inductances, capacitances), it is very difficult to form a filter which exhibits the largest attenuation or high isolation at a frequency f of a high frequency power source. Particularly, when the frequency f lies within a range from 10 MHz to 1 GHz, the circuit itself lies within a region where it changes from the concentrated constant circuit to the distributed constant circuit, and it is necessary to consider influences by both of them.